Method and apparatus for thermal analyses



Sept. 15, 1964 M. STOLL ETAL 3,148,531.

METHOD AND APPARATUS FOR THERMAL ANALYSES Filed Feb. 26, 1963 2Sheets-Sheet 1 T POWER SUPPLY SWITCH RECORDER IN VEN TORS ALICE M. STOLLLAMBERT R. MUNROE Sept. 15, 1964 s' ro ETAL 3,148,531

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r I I ATTORNEY United States Patent 3,148,531 METHUD AND APPARATUS FORTHERMAL ANALYSES Alice M. Stoll, Spring Vaiiey, and Lambert R. Munroe,Ambler, Pa, assignors to the United States of America as represented bythe Secretary of the Navy Filed Feb. 26, 1963, Ser. No. 261,237 Claims.(CI. 73-15) (Granted under Title 35, US. Code (I952), sec. 266) Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates to method and apparatus for determiningthe thermal properties of lightweight, thin fabrics or textiles whichare proposed or contemplated for use in garments worn in air and spacevehicles.

The speeds and altitudes now attainable or expected in existing andcontemplated high performance air and space vehicles has furtherextended mans environmenal demands, He may be subjected to ambienttemperatures that vary to wider extremes, and untoward exposure toflames from more volatile and high energy fuels. For example, followingan airplnae crash, the pilot may have to escape through an envelope offuel flames. Notwithstanding all of the precautions taken in vehicledesign to insure a safe and tolerable environment for man, his flyinggarments or space suit still remain his last and most fundamentalprotection against temperature extremes and flame exposure. Governmentprocurement of fabrics or textiles which will serve well under suchsevere thermal conditions has heretofore been impaired because noreliable and precise method or apparatus was available for assimilatingthese conditions with any degree of reproducibility and then impartingthem on the various thin fabrics or materials proposed by the textileindustry. Testing techniques and apparatus known in the prior art areincapable of yielding the accurate and consistent results which permitthe evaluations and fair comparisons of these thin materials ascontemplated by the present invention.

Accordingly, it is an object of the present invention to provide a novelmethod and apparatus for accurately determining thermal properties ofthin fabrics and other materials and with which lightweight textilescontaining new heat-resistant, nonflammable synthetic fibers may becompared as to their thermal diffusivity, conductivity and flamedestruction temperature.

Another object of the invention is to provide a new and improved methodand apparatus for determining the transient heat transfer properties ofsingle or multi-layer fabrics during flame exposure, in whichmulti-layer fabrics may be selected from a wide variety of combinationsin materials and structural arrangements, and in which the fabric isuniformly exposed to a desired flame intensity for a predeterminedduration, and in which the measured parameters are suitable for directthermodynamic analysis and comparison.

Still another object of the invention is to provide method and apparatusfor predicting the physiological effect on living skin protected by thinfabrics under severe thermal environments.

A further object of the invention is to provide a method and apparatusfor measuring thermal properties of materials subjected to areproducible thermal environment, which method can be carried out easilyand rapidly without degrading the accuracy of results, and whichapparatus is of relatively simple construction and is inexpensive tomaintain.

Various other objects and advantages will appear from the followingdescription of one embodiment of the invention, and the most novelfeatures will be particularly "ice pointed out hereinafter in connectionwith the appended claims.

In the drawings:

FIG. 1 is a mechanical and electrical schematic representation of oneembodiment of the apparatus of the present invention;

FIG. 2 is a fragmentary schematic representation of the apparatus takenalong the line 22 of FIG. 1;

FIG. 3 represents a more detailed electrical circuit diagram of theapparatus of FIG. 1;

FIG. 4 is a graphical representation of a typical timing sequence forthe apparatus as established in the electrical circuit of FIG. 3;

FIGS. 5a, 5b, and 50 represent enlarged cross-sectional views ofdifferent combinations and arrangements of material specimens to betested in the invention; and

FIG. 6 is a graphical correlation of thermal diflusivity andtemperature-time history for various materials.

In the illustrated embodiment of the invention, the apparatus shown inFIGS. 1 and 2 is set up for flame destruction temperature tests, and sowill be first described in connection therewith. In the situation wherea pilot flees from a flaming crash area, his garments may inflame ormelt and adhere to his skin. To evaluate fabrics as to these properties,the flame characteristics and exposure time is postulated. The inventionthen provides method and apparatus for carrying out the flamedestruction tests in the laboratory, based on these postulations, onvarious fabric specimens.

As best seen in FIG. 1 with the enlargement in FIG. 2, the apparatus isin a deenergized start or FLAME-OUT position with a thin fabric orspecimen S held securely in a specimen holder 10 which in turn isremovably mounted on an elongated carriage, indicated generally by thenumeral 11. The carriage 11 rests in a generally horizontal plane and isslidable along its length on a support means not shown from theFLAME-OUT position illustrated to a FLAME-IN position where the specimenS is directly in a flame region. The holder 10 is particularly adaptedfor performing flame destruction temperature tests because it simplysupports the specimen S without any backing. Other specimen holders suchas shown in FIGS. 5a, b and c are adapted to be substituted for theflame destruction test holder 1% when transient heat transfer propertiesof a specimen are being determined, as disclosed hereinbelow.

The carriage 11 is positioned over a burner 12, such as a Meker orBunsen type which is adjustable to provide a steady-state, uniformlydistributed circular flame. A carriage spring 14 secured at one end ofthe carriage 11 urges the latter to the FLAME-OUT position. The armatureof a solenoid operated motor 13 when energized drives the carriage 11 inthe opposite direction against the force of the spring 14 until thecarriage 11 is in the FLAME-IN position and the specimen S is directlyover the burner 12.

Prior to a test exposure of the specimen S it is important that theflame be uniform and in a desired steadystate condition of temperatureand heat generation. To assist in accomplishing this, the burner 12 isconnected through a flow meter 16 and manually adjustable control valve17 to a fuel supply 18 such as propane-propylene gas. With the carriage11 in the FLAME-OUT position, the flame will impinge upon the lowersurface of a high temperature resistant window 19, made of transparentmica or the like, which is supported in a carriage cross member 21.Thus, the flame can be easily viewed while adjusting for a desired flamecondition. The window 19 also prevents the flame so formed fromprojecting upward through the carriage 11 while the specimen S is out ofthe flame. A thermocouple T may be added on the lower side of the holder10 adjacent to the specimen S to provide a record representative offlame temperatures during the flame exposure, and a thermocouple T maybe added on the upper surface of the specimen S to provide a check offlame destruction temperatures. Appropriate terminals are provided onthe holder 10 for making connections to a high speed time-temperaturerecorder 33.

When the motor 13 is energized and positions the specimen S over theburner 12, an arm 22 projecting from the carriage 11 engages andactuates an electric switch 23 such as a Micro-switch and Whose functionis explained hereinbelow. The carriage 11 further includes a rigidextension 24 for supporting a solenoid operated motor 26 whose armatureis drivingly connected to guillotinetype slidable flame cut-off shutter27. When the motor 26 is deenergized, the shutter 27 is urged totallyout of the flame region irrespective of the carriage 11 position by ashutter spring 28. The flame cutting edge of the shutter 27 defines asemicircular notch 29 equal to the flame diameter thereby approachinginstantaneous flame cut-ofl when the shutter 27 traverses over theburner 12.

Measurement of the flame destruction temperature of the specimen S isaccomplished by a tilted mirror 31 positioned directly over the burner12 which reflects the radiant energy from the specimen S to a radiationdetecting head 3-2 whose output is connected to the time-temperaturerecorder 33. An optical filter 34 on the head 32 blocks all visibleWavelengths to provide only measurements of the temperature of the uppersurface of the specimen S during flame contact at its lower surface. Arotary solenoid operated motor 36 electrically connected to the switch23 positions a radiation cut-off shutter 37 out of the radiant energypath when the carriage 11 has moved the specimen S into the flameregion. A spring 38 urges the shutter 37 in front of the radiation head32 when the motor 36 is deenergized.

this position, the carriage arm 22 causes the switch 23 to close andenergize the radiation shutter motor 36. The shutter 37 moves to providean unobscured view by the head 32 of the upper surface of the specimenS. At the position b, the timer contact 47 closes to energize theshutter motor 26 thereby blocking further flame impingement to the undersurface of the specimen S. At the position 0, the timer contact 44 opensto deenergize both motors 13 and 36 and allows springs 14 and 33 to urgethe carriage 11 and the shutter 37, respectively, to the FLAME-OUTposition. The flame shutter 27 is urged by the spring 28 back to itsstart position and the timers 43 and 46 are automatically reset when themanual switch 41 is opened. During the interval when the specimen S isin the flame, the temperature on the upper surface of the specimen S ismeasured by the radiation head 32 and thermocouple T on the recorder 33.

It is contemplated that in most flame temperature destruction tests thetemperature measured at the instant of total penetration of the flamethrough the garment is of more interest than a temperature risemeasurement. In these instances the time interval a-b is set at someamount which will not interfere with flame impingement until afterpenetration.

In addition to flame temperature destruction testing, the invention isalso useful in determining the transient heat transfer properties ofvery thin fabrics. A better understanding and appreciation of thisportion of the invention will be obtained from a preliminarythermodynamic anaylsis of transient heat transfer through twolayerWalls.

An equation for transient heat flow through a twolayer wall has beenexpressed by Griflith and Horton in Proceedings of the Physical Society(London), vol. 58, page 481 et seq, 1946, as follows:

The electricity for operating the motors 13, 26 and 36 obtains from apower supply 39 through a manually operated switch 41 and a timer unit42, shown in more detail in FIG. 3. In the steps and operations of theinvention, there are three distinct events, two of which arepredetermined and set into the timer unit 42. These events aregraphically illustrated in FIG. 4 wherein the time point a representsthe instant when the manual switch 41 is closed and the specimen S movesfrom the position shown in FIG. 1 to the FLAME-IN position. At the timepoint b, the flame cut-off shutter 27 blocks the flame from the specimenS, and at the time point c, the specimen S is removed from the flame tothe FLAME-OUT position. The time interval ac is determined by anadjustable timer 43 and its normally closed contact 44 which opens atexpiration of the time set; and the time interval ab is determined by anadjustable timer 46 and its normally open contact 47 which closes atexpiration of the time set.

A flame temperature destruction test sequence should now be apparent. Inthe FLAME-OUT position shown in FIG. 1, and with the specimen S securedin the holder 10, a desired flame exposure time a-b is set on the timer46, and a time interval a-c is set on the timer 43 at some slightlygreater value. The flame from the burner 12 is also adjusted for thedesired steady-state condition by the adjustment of the valve 17 and theburner 12. The apparatus is now ready for test.

When the manual switch 41 is closed at time point a, the timers 43 and46 are started and the carriage motor 13 is energized through thenormally closed contact 44 thereby driving the specimen S into thefiarne region. At

m/D z wherein subscripts 1 and 2 refer to the adjacent exposed and baselayers, respectively,

The factor 7 in Equation 1 represents:

kgS k1S kgS2 wherein k thermal conductivity, and S volume specific heat(specific heat dcnsity).

Equation 2 differs from Griffith and Hortons equation only to the extentof What may be a more precise mathematical procedure.

The mathematical constant A obtains from Now, for a particular set ofconstant test conditions wherein the thermal properties of a constantbase layer are known, and the heat flux H, exposure time t, andthickness x and a are preselected, the diflusity D of the exposed layercan be plotted against the base layer temperature rise U for variouscombinations of thermal conductivity k, and volume specific heat S Acurve so plotted is shown in FIG. 6. t should now be apparent that thediffusivity D of any material used as the exposed layer can bedetermined directly from the temperature rise U of the constant baselayer so long as the test conditions are the same as those used inplotting the curve of FIG. 6.

FIG. 50 illustrates a transient heat transfer test arrangement for asingle-layer specimen S, the thicknesses c and x appropriatelyidentified. The thermocouple T represents the means for measuring thetemperature rise in the base layer. As in the flame temperaturedestruction tests, thermocouple T serves as a flame temperature checkduring FLAME-IN positioning. FIGS. 5a and 5b illustrate the thicknessparameters or and x for two differ.- ent materials S and S with andwithout an air space therebetween. The invention thus contemplates themeasurement of the average diffusivity of any combination of materialsso long as the aforementioned test conditions remain the same as usedfor plotting the curve as shown in FIG. 6.

Procedures for carrying out direct transient heat transferdeterminations are substantially the same as described above for flametemperature destruction tests except that the radiation head 32 is notused. Instead, a temperature is measured in the base layer by thethermocouple T Referring again to FIG. 50, the specimen S is securedbeneath a rigid base layer 48 of known thermal properties. Thethermocouple T is imbedded in the layer 48 a known distance from theinterface between the base layer 48 and the specimen S, hence theparameters of x and a as defined in Equation 1 are known. Thethermocouple T is included merely for observing flame conditions duringexposure of the specimen S. Additional thermocouples, such as T at theinterface, may be situated at other points of interest.

After establishing a desired flame condition, the manual switch 41 isclosed. The specimen S then moves over the flame region for the presettime during which the thermocouple T will sense and transmit to therecorder 33 the temperature rise U as it occurs. This temperature rise Uis then correlated on a curve such as shown in FIG. 6 for directlydetermining the diffusivity D of the specimen S without extensivecomputations such as discussed in connection with Equation 1.

It is further contemplated that the base layer 48, FIGS. 5a, 5b and 50,may be chosen with thermal properties similar to living skin in orderthat test conditions closely approximating those of a pilot wearing agarment made of specimen S or S and S" may be obtained.

It should now be apparent that the present method and apparatus providea very rapid means for empirically determining the thermal properties ofvarious materials, particularly very thin fabrics and textiles. Noextensive mathematical computations are involved. The invention iscapable of assimilating a variety of actual thermal environments, at thesame permitting these environments to be reproduced with a high degreeof accuracy. The invention is particularly applicable to directdeterminations of the destruction temperature of thin materials, theirheat transfer characteristics, and their insulation effect when airspaces are placed between layers thereof. Moreover, the presentlydisclosed method and apparatus permits analyses of thermal properties ofmaterials in contact with living tissues. Such data are of inestimablevalue in solving physiological problems concerning heat flow into livingskin where temperatures at shallow depths cannot otherwise be accuratelymeasured.

It will be understood, of course, that various changes in the details,materials, steps and arrangement of parts, which have been hereindescribed and illustrated in order 6 to explain the nature of theinvention, may be made by those skilled in the art Within the principleand scope of the invention as expressed in the appended claims.

What is claimed is:

1. A method for rapidly determining the transient heat transferproperties of thin fabrics, comprising the steps of:

mounting the fabric on a base of known thermal properties,

establishing a uniform steady-state flame of known heat flux,

exposing the outer side of the fabric to direct contact with said flame,

measuring the temperature rise in said base at a known distance from theinterface of said fabric and base during the flame exposure, and

removing the fabric from exposure after expiration of a predeterminedtime;

whereby the temperature rise so measured is a direct function of thethermal diffusivity of the fabric.

2. A method for rapidly determining the transient heat transferproperties of thin material, comprising the steps of:

mounting the material on a base of known thermal properties,

exposing the outer side of the material to direct contact with a uniformflame for a predetermined duration, and

measuring the temperature rise in said base at a known distance from theinterface of said material and base during the flame exposure;

whereby the temperature rise so measured is a direct function of thethermal diffusivity of the material.

3. A method for rapidly determining the transient heat transferproperties of thin materials, comprising the steps of:

mounting the material on a base of known thermal properties,

exposing the outer side of the material to a flame, and

measuring the temperature rise in said base at a known distance from theinterface of said material and base during the flame exposure.

4. Apparatus for determining thermal properties of thin fabrics,comprising:

a burner for establishing a uniform steady-state flame of known heatflux,

a carriage slidable relative to said burner in a horizontal planeselectively over the flame,

a holder supported in said carriage and formed to secure a specimen offabric thereto,

a first spring-return electric motor drivingly connected to saidcarriage for normally positioning said carriage so that said specimen isout of said flame until energized,

a flame shutter slidable in said carriage for selectively blocking theflame from said specimen irrespective of the position of said carriage,

a second spring-return electric motor drivingly connected to said flameshutter for normally positioning said shutter out of the blockingposition until energized,

a radiation responsive means positioned for measuring the temperature onthe upper side of the specimen when positioned in said flame region bysaid carriage,

a radiation shutter positioned for selectively blocking the radiationfrom said specimen,

a third spring-return electric motor drivingly connected to saidradiation shutter for normally positioning said radiation shutter in ablocking position until energized,

first switch means positioned relative to said carriage and electricallyconnected to said third motor for energizing the latter when saidspecimen is positioned in the flame region,

first automatic-reset timer means electrically connected to said firstmotor and said first switch for energizing said first and third motorsfor a predetermined time interval,

second automatic-reset timer means electrically connected to said secondmotor for maintaining electrical energy thereto for a time duration notgreater than the time interval set on said first timer means, and

second switch means electrically connected between a power supply andsaid first and second timers for selectively energizing said timers.

5. Apparatus as set forth in claim 4 wherein said holder furthercomprises:

a base made of a material having thermal properties similar to livingskin and formed to secure the specimen thereunder for flame exposure,and

a thermocouple imbedded in said base at a known distance from theinterface of said base and said specimen.

6. Apparatus for determining thermal properties of thin materialcomprising:

a burner for establishing a uniform steady-state flame of known heatflux,

carriage slidable relative to said burner in a horizontal planeselectively over the flame and formed to secure a specimen of materialthereto,

a first electric motor drivingly connected to said carriage for normallypositioning said carriage so that said specimen is out of said flameuntil energized,

a flame shutter slidable in said carriage for selectively blocking theflame from said specimen irrespective of the position of said carriage,

a second electric motor drivingiy connected to said flame shutter fornormally positioning said shutter out of the blocking position untilenergized,

a radiation responsive means positioned for measuring the temperature onthe upper side of the specimen when positioned in said flame region bysaid carriage,

a radiation shutter positioned for selectively blocking the radiationfrom said specimen,

a third electric motor drivingly connected to said radiation shutter fornormally positioning said radiation shutter in a blocking position untilenergized,

first switch means positioned relative to said carriage and electricallyconnected to said third motor for energizing the latter when saidspecimen is positioned in the flame region,

first timer means electrically connected to said first motor and saidfirst switch for energizing said first and third motors for apredetermined time interval,

second timer means electrically connected to said second motor formaintaining electrical energy thereto for a time duration not greaterthan the time interval set on said first timer means, and

second switch means electrically connected between a power supply andsaid first and second timers for selectively energizing said timers.

7. Apparatus as set forth in claim 6 wherein said carriage furthercomprises:

a base made of a material having thermal properties similar to livingskin and formed to secure the specimen thereunder for flame exposure,and

a thermocouple imbedded in said base at a known distance from theinterface of said base and said specimen.

8. Apparatus for determining thermal properties of thin materials,comprising:

a burner for establishing a uniform steady-state flame of known heatflux,

a. carriage slidable relative to said burner in a horizontal planeselectively over the flame and formed to secure a specimen of materialthereto,

a first electric means drivingly connected to said carriage for normallypositioning said carriage so that said specimen is out of said flameuntil energized,

a flame shutter slidable in said carriage for selectively blocking theflame from said specimen irrespective of the position of said carriage,

a second electric means drivingly connected to said flame shutter fornormally positioning said shutter out of the blocking position untilenergized,

a temperature responsive means positioned on the upper side of thespecimen,

first timer means electrically connected to said first motor forenergizing the latter for a predetermined time interval,

second timer means electrically connected to said second motor formaintaining electrical energy thereto for a time duration not greaterthan the time interval set on said first timer means, and

switch means electrically connected between a power supply and saidfirst and second timers for selectively energizing said timers.

9. Apparatus as set forth in claim 8 wherein said carriage furthercomprises:

a base made of a material having thermal properties similar to livingskin and formed to secure the specimen thereunder for flame exposure.

10. Apparatus for determining thermal properties of thin material,comprising:

a burner,

a carriage slidable relative to said burner selectively over the flameand formed to secure a specimen of material thereto,

a flame shutter slidable in said carriage for selectively blocking theflame from said specimen irrespective of the position of said carriage,

a temperature responsive means positioned for measuring the temperatureon the upper side of the specimen when positioned in said flame regionby said carriage,

first timer means operatively connected to said carriage for positioningsaid specimen in the flame for a predetermined time interval,

second timer means operatively connected to said flame shutter forpositioning said shutter in the flame after a time duration not greaterthan the time interval established by said first timer means, and

switch means electrically connected between a power supply and saidfirst and second timers for selectively energizing said timers.

References Cited in the file of this patent UNITED STATES PATENTS KimeSept. 4, 1951 Hager July 24, 1962 fer, N.Y., D. Van Nostrand Co., Inc,1957, pp. 5 and 6.

10. APPARATUS FOR DETERMINING THERMAL PROPERTIES OF THIN MATERIAL,COMPRISING: A BURNER, A CARRIAGE SLIDABLE RELATIVE TO SAID BURNERSELECTIVELY OVER THE FLAME AND FORMED TO SECURE A SPECIMEN OF MATERIALTHERETO, A FLAME SHUTTER SLIDABLE IN SAID CARRIAGE FOR SELECTIVELYBLOCKING THE FLAME FROM SAID SPECIMEN IRRESPECTIVE OF THE POSITION OFSAID CARRIAGE, A TEMPERATURE RESPONSIVE MEANS POSITIONED FOR MEASURINGTHE TEMPERATURE ON THE UPPER SIDE OF THE SPECIMEN WHEN POSITIONED INSAID FLAME REGION BY SAID CARRIAGE,